For cutting cast irons except for the FC material, namely materials such as the FCD, FCV, CGI, and ADI materials that are difficult-to-cut cast irons, generally low-speed processing (cutting speed V is 200 m/min or lower) is employed for which an insert coated with cemented carbide is used. In some cases, with the aim of improving the cutting speed, a cutting insert formed of a sintered body containing CBN (CBN sintered body) may be employed to cut a difficult-to-cut cast iron. Even if the cutting insert formed of a CBN sintered body is used, however, the cutting speed increased to 400 m/min or more will cause a rapid progression of wear and/or chipping of the cutting insert, resulting in a problem that cutting at a higher speed is difficult to achieve.
Further, in the case of cutting of the FC material (except for centrifugal cast iron), some manufacturers use a cutting insert formed of a CBN sintered body having a CBN content of 85% by volume or more, namely a so-called high-CBN-content sintered body, to practically perform high-speed continuous processing at cutting speed V of 1000 m/min or more. When the difficult-to-cut cast iron is cut, however, the temperature of the edge of the cutting insert is prone to increase while cutting is done. If a cutting insert is employed that is formed of a high-CBN-content sintered body with a high content of CBN having high reactivity with iron, wear of the cutting insert progresses at a considerably high rate. A resultant problem is therefore that, for cutting of the difficult-to-cut cast iron, the cutting insert formed of a high-CBN-content CBN sintered body is difficult to successfully employ. In order to avoid this problem, the difficult-to-cut cast iron is cut using a cutting insert formed of a sintered body of a ceramic material such as TiC (titanium carbide), Al2O3 (alumina), Si3N4 (silicon nitride), or SiAlON (sialon), or a CBN sintered body produced by mixing the powder of any of these ceramic materials and CBN particles and sintering them at an ultrahigh pressure (so-called low-CBN-content CBN sintered body). The cutting speed, however, is still restricted to 400 m/min or less under the current circumstances as described above.
Meanwhile, contouring is known to cut a workpiece using a cutting tool having a cutting insert. Specifically, the cutting tool makes revolutions while rotating about its axis so that the cutting insert is intermittently brought into contact with the workpiece (see for example Japanese Patent Laying-Open Nos. 11-347803 (PTL 1) and 8-39321 (PTL 2)).